Make legacy_or_psa.h public.

As a public header, it should no longer include common.h, just use
build_info.h which is what we actually need anyway.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/oid.c b/library/oid.c
index 4ecf621..dcd1815 100644
--- a/library/oid.c
+++ b/library/oid.c
@@ -27,7 +27,7 @@
 #include "mbedtls/rsa.h"
 #include "mbedtls/error.h"
 
-#include "legacy_or_psa.h"
+#include "mbedtls/legacy_or_psa.h"
 
 #include <stdio.h>
 #include <string.h>